Current mode bus interface system, method of performing a mode transition and mode control signal generator for the same

ABSTRACT

A current mode bus interface system includes a host interface device configured to transmit a reference current and a clock current, and to transmit a data current during a first transfer mode, and to receive a reverse direction data current and compare the reverse direction data current with the reference current to generate a reverse direction data voltage during a second transfer mode; and a client interface device configured to receive the reference current and the clock current and compare the reference current with the clock current to generate a clock voltage, to receive the data current and compare the data current with the reference current to generate a data voltage during the first transfer mode, and to transmit the reverse direction data current through a conducting wire over which the data current is received during the second transfer mode.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of co-pending U.S. application Ser. No.11/357,550, filed Feb. 17, 2006, which claims foreign priority under 35U.S.C. § 119 to Korean Patent Application No. 2005-19050 filed Feb. 17,2006, which is hereby incorporated by reference for all purposes as iffully set forth herein.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a bus interface system, and moreparticularly to a current mode bus interface system thattransmits/receives data currents.

2. Discussion of Related Art

Generally, to transmit/receive signals between integrated circuits,either a voltage mode transmitting/receiving operation or a current modetransmitting/receiving operation is performed. Since the voltage modetransmitting/receiving operation introduces a resistive-capacitive delaywhen transmitting/receiving signals, the current modetransmitting/receiving operation has been studied to reduce theresistive-capacitive delay.

In the current mode transmitting/receiving operation, a current of atransmitted/received signal is observed. In particular, the current modetransmitting/receiving operation maintains a voltage level of atransmission line at a predetermined level, and transfers data bychanging a level of a current flowing through the transmission line. Forexample, a transmitter may sequentially transfer digital data using twologic levels ‘1’ and ‘0’. Thus, a current level of about 17 mA through23 mA may be set to the logic level ‘1’, and a current level of about 0mA through 6 mA may be set to the logic level ‘0’. A receiver may thenrecover the transmitted digital data by determining the current level ofthe transmitted signals. Since the voltage level is maintained at thepredetermined level during the current mode transmitting/receivingoperation, a resistive-capacitive delay may be reduced.

In a ‘pseudo-differential current mode’ transmitting/receivingoperation, the transmitter may transmit a reference current with a datacurrent. For example, the transmitter may set the current level of about17 mA through 23 mA to the logic level ‘1’, set the current level ofabout 0 mA through 6 mA to the logic level ‘0’, and transmit the datacurrent based on the set logic levels. At the same time, the transmittermay transmit a reference current of about 10 mA. The receiver receivesboth the data current and the reference current, compares a magnitude ofthe data current with that of the reference current, and then determinesthe logic level of the transmitted data current. Thus, for example, whenthe magnitude of the data current is larger is than that of thereference current, the transmitted digital data is the logic level ‘1’,and when the magnitude of the data current is smaller than that of thereference current, the transmitted digital data is the logic level ‘0’.

In a device embodying a mobile application such as a portable phone, abus interface can be used to aid in the reduction of power consumption.For example, by causing the bus interface and other components of thedevice to enter into a suspend mode when they are not being used, thepower consumed by the device may be reduced. Accordingly, as variousapplications and devices such as a mobile phone and a digital cameracontinue to become integrated, the need to support bidirectional datatransfer between a digital camera module and a mobile phone module isincreasing. However, because the bus interface is increasingly beingused in such devices, the ability to conserve power is lessened. Assuch, a need exists for a bus interface system that is capable ofperforming a bidirectional data transfer between a host and a clientwhile reducing power consumption.

SUMMARY OF THE INVENTION

In an embodiment of the present invention, a current mode bus interfacesystem includes: a host interface device configured to transmit areference current and a clock current, and to transmit a data currentduring a first transfer mode, and to receive a reverse direction datacurrent and compare the reverse direction data current with thereference current to generate a reverse direction data voltage during asecond transfer mode; and a client interface device configured toreceive the reference current and the clock current and compare thereference current with the clock current to generate a clock voltage, toreceive the data current and compare the data current with the referencecurrent to generate a data voltage during the first transfer mode, andto transmit the reverse direction data current through a conducting wireover which the data current is received during the second transfer mode.

In another embodiment of the present invention, a current mode hostinterface device includes: a reference current transmitter configured totransmit a reference current; a clock current transmitter configured totransmit a clock current that periodically changes; and a datatransmitter/receiver configured to transmit a data current during aforward direction transfer mode, and to receive a reverse direction datacurrent through a conducting wire over which the data current istransmitted and compare the reference current with the reverse directiondata current to generate a reverse direction data voltage during areverse direction transfer mode.

The current mode host interface device may cut off the reference currentand cause the clock current and the data current to enter into a suspendmode in response to a sleep request. The current mode host interfacedevice may perform a transition from the suspend mode to a normaloperation mode in response to the wake-up request, or when a receptionof the reverse direction data current having a predetermined level issensed. The current mode host interface device may transmit thereference current to the current mode client interface device when thecurrent mode host interface device performs the transition from thesuspend mode to the normal operation mode, and may transmit the clockcurrent and the data current after the current mode client interfacedevice performs the transition from the suspend mode to the normaloperation mode.

In yet another embodiment of the present invention, a current modeclient interface device includes: a clock voltage generator configuredto receive a reference current and a clock current that periodicallychanges and compare the reference current with the clock current togenerate a clock voltage; and a data transmitter/receiver configured toreceive a data current and compare the reference current with the datacurrent to generate a data voltage during a forward direction transfermode, and to transmit a reverse direction data current through aconducting wire over which the data current is received during a reversedirection transfer mode.

The current mode client interface device may further include a modecontrol signal generator configured to sense the reference current togenerate a mode control signal.

In another embodiment of the present invention, a method of performing amode transition in a current mode bus interface system includes: cuttingoff transmitted currents from a host when the host enters into a suspendmode in response to a sleep request from the host; causing a client toenter into a suspend mode when the client senses the cut-off of thetransmitted currents; and causing the host or the client to perform atransition from the suspend mode to a normal operation mode in responseto a wake-up request from the host or the client.

The normal operation mode includes a forward direction transfer mode anda reverse direction transfer mode. The transmitted currents may includea reference current, a clock current and a data current, and the clientmay enter into the suspend mode when the client senses the cut-off ofthe reference current. Both the host and the client may generate thewake-up request to perform the transition from the suspend mode to thenormal operation mode.

In yet another embodiment of the present invention, a mode controlsignal generator of a current mode bus interface system includes: areceived current copier configured to copy a received current togenerate a copied received current; a comparing current generatorconfigured to generate a comparing current having a magnitude smallerthan a magnitude of the received current; a current comparatorconfigured to compare the copied received current with the comparingcurrent to generate a comparison signal; and a noise cancellation unitconfigured to cancel a noise component included in the comparison signalto generate a mode control signal.

The received current may be a reference current transmitted from a hostof the current mode bus interface system. The comparing current may begenerated by using the reference current stored as a digital value.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which like reference numbers referto like elements throughout:

FIG. 1 is a block diagram illustrating a current mode bus interfacesystem according to an exemplary embodiment of the present invention;

FIG. 2 is a block diagram illustrating a current mode host interfacedevice shown in FIG. 1;

FIG. 3 is a block diagram illustrating a current mode client interfacedevice shown in FIG. 1;

FIG. 4 is a block diagram illustrating a mode control signal generatorshown in FIG. 3;

FIG. 5A shows a waveform having a noise component;

FIG. 5B shows a waveform having a noise component;

FIG. 6 is a circuit diagram illustrating a noise cancellation circuitshown in FIG. 4 according to an exemplary embodiment of the presentinvention;

FIG. 7 is a circuit diagram illustrating the noise cancellation circuitshown in FIG. 4 according to another exemplary embodiment of the presentinvention;

FIG. 8 is a timing diagram illustrating a transition from a normaloperation mode to a suspend mode according to an exemplary embodiment ofthe present invention; and

FIGS. 9 through 11 are timing diagrams illustrating transitions from asuspend mode to a normal operation mode according to other exemplaryembodiments of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will beexplained in detail with reference to the accompanying drawings.However, specific structural and functional details disclosed herein aremerely presented for purposes of describing the exemplary embodiments ofthe present invention.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will also be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between”, “adjacent” versus “directlyadjacent”, etc.).

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of the invention. As usedherein, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising”, “includes” and/or “including”, when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

FIG. 1 is a block diagram illustrating a current mode bus interfacesystem 100 according to an exemplary embodiment of the presentinvention.

Referring to FIG. 1, the current mode bus interface system 100 includesa current mode host interface device 110 and a current mode clientinterface device 120. Hereinafter, the current mode host interfacedevice 110 and the current mode client interface device 120 may bereferred to as a host 110 and a client 120, respectively.

The current mode host interface device 110 transmits a reference currentIREF and a clock current ICLK to the current mode client interfacedevice 120. The current mode host interface device 110 also transmits adata current IDATA to the current mode client interface device 120during a forward direction transfer mode. The current mode hostinterface device 110 receives a reverse direction data current IR_DATAfrom the current mode client interface device 120 and compares thereverse direction data current IR_DATA with the reference current IREFto generate a reverse direction data voltage.

The current mode client interface device 120 receives the referencecurrent IREF and the clock current ICLK from the current mode hostinterface device 110, and compares the reference current IREF with theclock current ICLK to generate a clock voltage. The current mode clientinterface device 120 receives the data current IDATA from the currentmode host interface device 110 during the forward direction transfermode, and compares the data current IDATA with the reference currentIREF to generate a data voltage. In addition, the current mode clientinterface device 120 transmits the reverse direction data currentIR_DATA to the current mode host interface device 110 through aconducting wire over which the data current IDATA is received during areverse direction transfer mode.

As shown, for example, in FIG. 1, when the clock current ICLK, the datacurrent IDATA and the reverse direction data current IR_DATA have acurrent level of about 300 μA they may be set to a logic ‘high’ level,and when other currents have a current level of about 100 μA they may beset to a logic ‘low’ level. The reference current IREF may have acurrent level of about 200 μA and since the amount of data transferredfrom the client 120 to the host 110 is typically smaller than thattransferred from the host 110 to the client 120 the reverse directiondata current IR_DATA may have a frequency lower than that of the datacurrent IDATA.

FIG. 2 is a block diagram illustrating the current mode host interfacedevice 110 shown in FIG. 1.

Referring to FIG. 2, the current mode host interface device 110 includesa reference current transmitter 210, a clock current transmitter 220 anda data transmitter/receiver 230.

The reference current transmitter 210 transmits the reference currentIREF. The reference current transmitter 210 includes a current source211 for generating the reference current IREF.

The reference current IREF generated by the current source 211 may flowto the host 110 from the client 120, or to the client 120 from the host110.

The clock current transmitter 220 transmits the clock current ICLK. Theclock current transmitter 220 includes a low current source 221, adifferential current source 222 and a clock control switch 223.

The low current source 221 provides a low current ILOW having half amagnitude of the reference current IREF. The differential current source222 provides a differential current IDIFF substantially identical to themagnitude of the reference current IREF.

The clock control switch 223 transmits the clock current ICLK, identicalto a magnitude of the low current ILOW or identical to a magnitude of asum of the low current ILOW and the differential current IDIFF, based ona clock control signal TXCLK.

For example, the reference current IREF and the differential currentIDIFF may have a current level of about 200 μA respectively. The lowcurrent ILOW may have a current level of about 100 μA. Consequently, theclock current ICLK may have a current level of about 100 μA or 300 μA.

The data transmitter/receiver 230 transmits the data current IDATAduring the forward direction transfer mode, and receives the reversedirection data current IR_DATA during the reverse direction transfermode and compares the reference current REF with the reverse directiondata current IR_DATA to generate a reverse direction data voltageTXRDATA.

The data transmitter/receiver 230 includes switches 231 and 232, a datacurrent transmitter and a data current receiver.

The switch 231 is closed during the forward direction transfer mode, andis opened during the reverse direction transfer mode.

Contrary to the switch 231, the switch 232 is closed during the reversedirection transfer mode, and is opened during the forward directiontransfer mode.

The data current transmitter transmits the data current IDATA via theswitch 231 during the forward direction transfer mode.

The data current transmitter includes a low current source 233, adifferential current source 234 and a data control switch 235.

The low current source 233 provides a low current ILOW having half themagnitude of the reference current IREF.

The differential current source 234 provides a differential currentIDIFF substantially identical to the magnitude of the reference currentIREF.

The data control switch 235 transmits the data current IDATA, identicalto a magnitude of the low current ILOW or identical to a magnitude of asum of the low current ILOW and the differential current IDIFF, based ona data control signal TXDATA.

For example, the reference current IREF and the differential currentIDIFF may have a current level of about 200 μA, respectively. The lowcurrent ILOW may have a current level of about 100 μA. Consequently, thedata current IDATA may have a current level of about 100 μA or 300 μA.

The data current receiver receives the reverse direction data currentIR_DATA via the switch 232 during the reverse direction transfer modeand then generates the reverse direction data voltage TXRDATA.

The data current receiver includes a reference current copier 236, adata current copier 237 and a current comparator 238.

The reference current copier 236 copies the reference current IREF togenerate a copied reference current IREF.

The data current copier 237 copies the reverse direction data currentIR_DATA to generate a copied reverse direction data current IR_DATA.

The reference current copier 236 and the data current copier 237 may beimplemented by using a current mirror.

The current comparator 238 compares the copied reference current IREFwith the copied reverse direction data current IR_DATA to generate thereverse direction data voltage TXRDATA.

The current comparator 238 may be implemented by using various methodsknown to one of ordinary skill in the art. For example, the currentcomparator 238 may be an operational amplifier.

As shown in FIG. 2, the current mode host interface device 110 may cutoff the reference current IREF, the clock current ICLK and the datacurrent IDATA to enter into a suspend mode in response to a sleeprequest. When the current mode host interface device 110 is in thesuspend mode it may perform a transition from the suspend mode to anormal operation mode when a wake-up request occurs or when the reversedirection data current IR_DATA having a predetermined current level isdetected.

When the current mode host interface device 110 performs the transitionfrom the suspend mode to the normal operation mode, the current modehost interface device 110 transmits the reference current IREF to thecurrent mode client interface device 120, and then, transmits the clockcurrent ICLK and the data current IDATA after the current mode clientinterface device 120 completes the transition from the suspend mode tothe normal operation mode.

FIG. 3 is a block diagram illustrating the current mode client interfacedevice 120 shown in FIG. 1.

Referring to FIG. 3, the current mode client interface device 120includes a clock voltage generator 310 and a data transmitter/receiver320. The current mode client interface device 120 may further include amode control signal generator 330.

The clock voltage generator 310 receives the reference current IREF andthe clock current ICLK, which may change periodically, and compares thereference current IREF with the clock current ICLK to generate a clockvoltage RXCLK.

The clock voltage generator 310 includes a reference current copier 340,a clock current copier 311 and a current comparator 312.

The reference current copier 340 copies the reference current IREF togenerate a copied reference current IREF.

The reference current copier 340 may be implemented by using a currentmirror, and may provide the copied reference current IREF to the currentcomparator 312, the data transmitter/receiver 320 and the mode controlsignal generator 330.

The clock current copier 311 copies the clock current ICLK to generate acopied clock current ICLK, and may be implemented by using a currentmirror.

The current comparator 312 compares the copied reference current IREFwith the copied clock current ICLK to generate the clock voltage RXCLK.

The data transmitter/receiver 320 receives the data current IDATA duringthe forward direction transfer mode and compares the reference currentIREF with the data current IDATA to generate a data voltage RXDATA.

The data transmitter/receiver 320 transmits the reverse direction datacurrent IR_DATA through a conducting wire over which the data currentIDATA is received during the reverse direction transfer mode.

The data transmitter/receiver 320 includes switches 321 and 322, a datacurrent transmitter and a data current receiver.

The switch 321 is closed during the forward direction transfer mode, andis opened during the reverse direction transfer mode.

Contrary to the switch 321, the switch 322 is closed during the reversedirection transfer mode, and is opened during the forward directiontransfer mode.

The data current transmitter transmits the reverse direction datacurrent IR_DATA via the switch 322 during the reverse direction transfermode.

The data current transmitter includes a low current source 323, adifferential current source 324 and a data control switch 325.

The low current source 323 provides a low current ILOW having half amagnitude of the reference current IREF.

The differential current source 324 provides a differential currentIDIFF substantially identical to the magnitude of the reference currentIREF.

The low current source 323 and the differential current source 324 maybe generated by using the reference current IREF stored as a digitalvalue to prevent a mismatch between a current quantity provided from thecurrent mode client interface device 120 and a current quantity beingconsidered by the current mode host interface device 110.

For example, due to temperature variations, manufacturing processvariations and supply voltage variations, the current mode hostinterface device 110 may not be able to distinguish data included in thereverse direction data current IR_DATA received from the current modeclient interface device 120 by using the reference current IREF. Toprevent this, the low current source 323 and the differential currentsource 324 may be generated by using the reference current IREF storedas a digital value. In particular, when the reference current IREF isstored as the digital value, an unnecessary current flow may beprevented Still referring to FIG. 3, the data control switch 325transmits the reverse direction data current IR_DATA, identical to amagnitude of the low current ILOW or identical to a magnitude of a sumof the low current ILOW and the differential current IDIFF, based on areverse direction data control signal RXRDATA.

For example, the reference current IREF and the differential currentIDIFF may have a current level of about 200 μA, respectively. The lowcurrent ILOW may have a current level of about 100 μA. Consequently, thereverse direction data current IR_DATA may have a current level of about100 μA or 300 μA.

The data current receiver receives the data current IDATA via the switch321 during the forward direction transfer mode and then generates thedata voltage RXDATA.

The data current receiver includes the reference current copier 340, adata current copier 326 and a current comparator 327.

The reference current copier 340 copies the reference current IREF togenerate a copied reference current IREF. The data current copier 326copies the data current IDATA to generate a copied reverse data currentIDATA.

The reference current copier 340 and the data current copier 326 may beimplemented by using a current mirror.

The current comparator 327 compares the copied reference current IREFwith the copied data current DATA to generate the data voltage RXDATA.The current comparator 327 may be implemented by using various methodsknown to one of ordinary skill in the art. For example, the currentcomparator 327 may be an operational amplifier.

The mode control signal generator 330 generates a mode control signalRXPD according to whether the reference current IREF is allowed to flowfrom the host 110 or is cut off by the host 110. For example, the modecontrol signal generator 330 may change a state of the mode controlsignal RXPD to a logic ‘high’ level when the reference current IREF isallowed to flow from the host 110, and may change the state of the modecontrol signal RXPD to a logic ‘low’ level when the reference currentIREF is cut off by the host 110.

The mode control signal. generator 330 of FIG. 3 may be included in thecurrent mode host interface device 110 as well as the current modeclient interface device 120. In such a case, the current mode hostinterface device 110 may detect a current transferred from the currentmode client interface device 120 to control its transition between thenormal operation mode and the suspend mode.

FIG. 4 is a block diagram illustrating the mode control signal generator330 shown in FIG. 3.

Referring to FIG. 4, the mode control signal generator 330 includes areference current copier (not shown), a comparing current generator 410,a current comparator 420, and a noise cancellation unit 430.

The reference current copier copies the reference current IREF togenerate a copied reference current IREF. Although not shown, thereference current copier may be implemented by using a current mirror,and may be included in or the same as the reference current copier 340shown in FIG. 3.

The comparing current generator 410 generates a comparing current IPDShaving a magnitude smaller than the reference current IREF.

When the magnitude of the comparing current IPDS is smaller than themagnitude of the reference current IREF, a current consumed during thenormal operation mode may be reduced and power consumption may therebybe reduced. However, when the magnitude of the comparing current IPDS ismuch smaller than the magnitude of the reference current IREF, themagnitude of the comparing current IPDS should be determined to be at alevel such that a noise characteristic of a comparison signal is notdegraded. For example, the level of the comparing current IPDS may bedetermined by performing a simulation.

The comparing current generator 410 may be implemented by using a diodecoupled CMOS transistor, or by using a current mirror.

The comparing current IPDS is generated by using the reference currentIREF and may correspond to a predetermined ratio of the referencecurrent IREF. For example, the comparing current IPDS may correspond toabout 10% of the reference current IREF. The comparing current generator410 may also generate the comparing current IPDS by using the referencecurrent IREF stored as a digital value.

Still referring to FIG. 4, the current comparator 420 compares thecopied reference current IREF with the comparing current IPDS togenerate the comparison signal. For example, when the reference currentIREF is allowed to flow from the host 110, a state of the comparisonsignal is a logic ‘high’ level, and when the reference current IREF iscut off by the host 110, the state of the comparison signal is a logic‘low’ level.

The current comparator 420 may be implemented by using various methodsknown to one of ordinary skill in the art. For example, the currentcomparator 420 may be an operational amplifier.

The comparing current generator 410 allows the comparing current IPDS toflow when the reference current IREF is allowed to flow from the host110, and does not allow the comparing current IPDS to flow, to reducepower consumption during the suspend mode, when the reference currentIREF is cut off by the host 110.

The noise cancellation unit 430 cancels a noise component included inthe comparison signal to generate the mode control signal RXPD of thecurrent mode client interface device 120.

The noise cancellation unit 430 is used to cancel noise included insignals transmitted, for example, through a current mode bus interfaceof the current mode bus interface system 100, thus preventing thecurrent mode bus interface system 100 from operating abnormally.

The mode control signal RXPD may also be used for controlling thetransition between the normal operation mode and the suspend mode of thecurrent mode client interface device 120. For example, the current modeclient interface device 120 may operate in the normal operation modewhen the mode control signal RXPD is at the logic ‘high’ level, and thecurrent mode client interface device 120 may operate in the suspend modewhen the mode control signal RXPD is at the logic ‘low’ level.

Hereinafter, operations of the mode control signal generator 330 shownin FIG. 4 will be explained.

When the current mode host interface device 110 performs the transitionfrom the normal operation mode to the suspend mode and cuts off thereference current REF, the current comparator 420 senses the cut-off ofthe reference current IREF by using the comparing current IPDS. When thecurrent comparator 420 senses the cut-off of the reference current IREFto generate the comparison signal, the noise cancellation unit 430cancels the noise component included in the comparison signal togenerate the mode control signal RXPD.

Additionally, when the current mode host interface device 110 performsthe transition from the suspend mode to the normal operation mode andallows the reference current IREF to flow to the client 120, the currentcomparator 420 senses the flow of the reference current IREF by usingthe comparing current IPDS and generates the mode control signal RXPDthrough the noise cancellation unit 430.

The noise cancellation unit 430 includes a Schmitt trigger circuit 431and a noise cancellation circuit 432.

The Schmitt trigger circuit 431 cancels the noise component having avoltage level smaller than a predetermined voltage level included in thecomparison signal.

The noise cancellation circuit 432 cancels the noise component of ashort pulse region included in the comparison signal.

FIG. 5A is a waveform diagram illustrating noise cancelled by theSchmitt trigger circuit 431 according to an exemplary embodiment of thepresent invention.

As shown in FIG. 5A, a noise component 510 having the voltage levelsmaller than the predetermined voltage level included in the comparisonsignal is cancelled by the Schmitt trigger circuit 431.

FIG. 5B is a waveform diagram illustrating noise cancelled by a noisecancellation circuit 432 according to another exemplary embodiment ofthe present invention.

As shown in FIG. 5B, a noise component 520 of a short pulse regionincluded in the comparison signal is cancelled by the noise cancellationcircuit 432.

FIG. 6 is a circuit diagram illustrating the noise cancellation circuit432 shown in FIG. 4 according to an exemplary embodiment of the presentinvention.

Referring to FIG. 6, the noise cancellation circuit 432 includes a CMOSinverter. The noise cancellation circuit 432 controls an aspect ratio(W/L) of a PMOS transistor 610 constituting the CMOS inverter to cancela noise component of a short pulse region.

FIG. 7 is a circuit diagram illustrating the noise cancellation circuit432 shown in FIG. 4 according to another exemplary embodiment of thepresent invention.

Referring to FIG. 7, the noise cancellation circuit 432 includes a delaysection 710 and an AND gate 720.

The delay section 710 delays the comparison signal. The AND gate 720performs a logical operation on the comparison signal and the comparisonsignal delayed by the delay section 710 to generate the mode controlsignal RXPD.

Accordingly, the noise cancellation circuit 432 shown in FIG. 7 maycancel a noise component of a pulse region shorter than a delayed timeperiod of the delay section 710.

FIG. 8 is a timing diagram illustrating a transition from a normaloperation mode to a suspend mode according to an exemplary embodiment ofthe present invention.

Referring to FIG. 8, a host mode control signal TXPD drops to the logic‘low’ level from the logic ‘high’ level in response to a sleep requestfrom the current mode host interface device 110.

When the host mode control signal TXPD drops to the logic ‘low’ level,the current mode host interface device 110 cuts off the referencecurrent IREF, the clock current ICLK and the data current IDATA.

A time period ‘tpd’ refers to a time during which the host mode controlsignal TXPD drops to the logic ‘low’ level from the logic ‘high’ level,and to a time during which the current mode host interface device 110cuts off the reference current IREF, the clock current ICLK and the datacurrent IDATA.

When the reference current IREF, the clock current ICLK and the datacurrent IDATA are cut off, the current mode client interface device 120senses the cut off and drops the client mode control signal RXPD to thelogic ‘low’ level. When the client mode control signal RXPD is at thelogic ‘low’ level, the current mode client interface device 120 entersinto the suspend mode and does not consume current.

In other words, the current mode client interface device 120 powers downeach module therein to prevent power consumption when the client modecontrol signal RXPD is at the logic ‘low’ level. It is to be understoodthat although the current mode client interface device 120 may sense thecut-off of the reference current IREF, the clock current ICLK and thedata current IDATA and enter into the suspend mode, the current modeclient interface device 120 may sense the cut-off of one of thereference current IREF, the clock current ICLK and the data currentIDATA and enter into the suspend mode. For example, the current modeclient interface device 120 may sense the cut-off of the referencecurrent IREF and enter into the suspend mode.

When the current mode host interface device 110 enters into the suspendmode, each of the modules generating the reference current IREF, theclock current ICLK and the data current IDATA enters into a sleep modeand thus power consumption does not occur. At this time, some of themodules may consume power to sense a wake-up signal when it is receivedfrom the current mode client interface device 120. For example, when thecurrent mode host interface device 110 is in the suspend mode, the datacurrent receiver may remain activated to sense the reverse directiondata current having a predetermined level. In addition, when the currentmode host interface device 110 includes the mode control signalgenerator 330, the mode control signal generator 330 may remainactivated to sense the wake-up signal when it is received from thecurrent mode client interface device 120 during the suspend mode.

When the current mode client interface device 120 enters into thesuspend mode, the clock voltage generator 310 and the datatransmitter/receiver 320 enter into the sleep mode, and thus the clockvoltage generator 310 and the data transmitter/receiver 320 do notconsume power. At this time, the mode control signal generator 330included in the current mode client interface device 120 may remainactivated to sense the wake-up signal when it is received from thecurrent mode host interface device 110.

FIGS. 9 through 11 are timing diagrams illustrating transitions from asuspend mode to a normal operation mode according to another exemplaryembodiment of the present invention.

In FIGS. 9 through 11, the timing diagrams of the control signals TXPDand RXPD represent a voltage level, and the timing diagrams of thereference current IREF, the clock current ICLK, the data current IDATAand the reverse direction data current IR_DATA represent a currentlevel.

FIG. 9 is a timing diagram illustrating a transition from the suspendmode to the normal operation mode of the current mode bus interfacesystem 100 in response to a wake-up request from the current mode hostinterface device 110.

Referring to FIG. 9, a state of the host mode control signal TXPD ischanged from the logic ‘low’ level to the logic ‘high’ level in responseto a wake-up request from the current mode host interface device 110.

When the state of the host mode control signal TXPD is changed from thelogic ‘low’ level to the logic ‘high’ level, the current mode hostinterface device 110 allows the reference current IREF that was cut offto flow to the client 120.

When the reference current IREF is allowed to flow to the client 120,the current mode client interface device 120 senses the referencecurrent IREF to change a state of the client mode control signal RXPDfrom the logic ‘low’ level to the logic ‘high’ level.

When the state of the client mode control signal RXPD is changed fromthe logic ‘low’ level to the logic ‘high’ level, the current mode clientinterface device 120 activates internal modules that were in the sleepmode and is changed to the normal operation mode.

The current mode host interface device 110 transmits the clock currentICLK and the data current IDATA after the current mode client interfacedevice 120 is changed to the normal operation mode and is then ready toreceive currents. In other words, the state of the client mode controlsignal RXPD is changed to the logic ‘high’ level from the logic ‘low’level within the time period ‘ttxa’ shown in FIG. 9.

The time period ‘ttxa’ refers to a time during which the current modehost interface device 110 allows the reference current IREF to againflow to the client 120, and to a time during which the current mode hostinterface device 110 allows the clock current ICLK and the data currentIDATA to again flow to the client 120.

After a time period ‘trxs’ has begun to elapse, which occurs, forexample, immediately after the time period ‘ttxa’, the waveforms of theclock current ICLK and the data current IDATA are changed.

FIG. 10 is a timing diagram illustrating a transition from the suspendmode to the normal operation mode of the current mode bus interfacesystem 100 in response to a wake-up request from the current mode clientinterface device 120.

Referring to FIG. 10, the client mode control signal RXPD is changed tothe logic ‘high’ level from the logic ‘low’ level in response to thewake-up request from the current mode client interface device 120.

When the state of the client mode control signal RXPD is changed to thelogic ‘high’ level from the logic ‘low’ level, the current mode clientinterface device 120 allows the reverse direction data current IR_DATAto flow to the host 110. At this time, the reverse direction datacurrent IR_DATA may be the logic ‘low’ level or the logic ‘high’ level.The reverse direction data current IR_DATA has a level sensed by thecurrent mode host interface device 110 by using the reference currentIREF.

When the reverse direction data current IR_DATA is allowed to flow tothe host 110, the current mode host interface device 110 senses the flowof the reverse direction data current IR_DATA to change the host modecontrol signal TXPD to the logic ‘high’ level from the logic ‘low’level. The current mode host interface device 110 may sense the reversedirection data current IR_DATA by using the mode control signalgenerator 330.

When the state of the host mode control signal TXPD is changed to thelogic ‘high’ level, the current mode host interface device 110 allowsthe reference current IREF that was cut off to flow to the client 120.

When the flow of the reference current IREF is started, the current modeclient interface device 120 senses the reference current REF andactivates internal modules that were in the sleep mode to perform thetransition to the normal operation mode. At this time, the current modeclient interface device 120 stops to transmit the reverse direction datacurrent IR_DATA to the host 110, and changes the transfer mode of thedata transmitter/receiver 320 to the forward direction transfer mode.

The current mode host interface device 110 transmits the clock currentICLK and the data current IDATA after the current mode client interfacedevice 120 is changed to the forward direction transfer mode and isready to receive transmitted currents. In other words, the current modeclient interface device 120 is changed to the forward direction transfermode within the time period ‘ttxa’ shown in FIG. 10.

The time period ‘ttxa’ refers to a time during which the current modehost interface device 110 allows the reference current IREF that was cutoff to again flow to the client 120, and to a time during which thecurrent mode host interface device 110 allows the clock current ICLK andthe data current IDATA to again flow to the client 120. A time period‘trxd’ refers to a time during which the current mode host interfacedevice 110 allows the reference current IREF that was cut off to againflow to the client 120, and to a time during which the current modeclient interface device 120 cuts off the reverse direction data currentIR_DATA.

FIG. 11 is a timing diagram illustrating a transition to a normaloperation mode of the current mode interface system 100 when the currentmode host interface device 110 and the current mode client interfacedevice 120 nearly simultaneously generate a wake-up request.

Referring to FIG. 11, the state of the client mode control signal RXPDis changed to the logic ‘high’ level from the logic ‘low’ level inresponse to the wake-up request, and nearly simultaneously, the state ofthe host mode control signal TXPD is changed to the logic ‘high’ levelfrom the logic ‘low’ level in response to the wake-up request.

Because the state of the host mode control signal TXPD is changed to thelogic ‘high’ level from the logic ‘low’ level, the current mode hostinterface device 110 allows the reference current IREF to flow to theclient 120, and because the state of the client mode control signal RXPDis changed to the logic ‘high’ level from the logic ‘low’ level, thecurrent mode client interface device 120 allows the reverse directiondata current IR_DATA to flow to the host 110.

After the current mode host interface device 110 allows the referencecurrent IREF to flow to the client 120, the current mode host interfacedevice 110 senses the reverse direction data current IR_DATA; however,the current mode host interface device 110 is changed to the forwarddirection transfer mode since the current mode host interface device 110allows the reference current IREF to flow to the client 120.

After the current mode client interface device 120 allows the reversedirection data current IR_DATA to flow to the client 120, the currentmode client interface device 120 senses the reference current IREF toactivate internal modules that were in the sleep mode, and is changed tothe normal operation mode. At this time, the current mode clientinterface device 120 stops to transmit the reverse direction datacurrent IR_DATA to the host 110 and changes the transfer mode of thedata transmitter/receiver 320 to the forward direction transfer mode.

After the transfer mode of the current mode client interface device 120is changed to the forward direction transfer mode and the current modeclient interface device 120 is ready to receive transmitted currents,the current mode host interface device 110 transmits the clock currentICLK and the data current IDATA to the client 120. In other words, thecurrent mode client interface device 120 is changed to the forwarddirection transfer mode from the reverse direction transfer mode withina time period ‘ttxa’ shown in FIG. 11. The time period ‘ttxa’ refers toa time during which the current mode host interface device 110 allowsthe reference current IREF that was cut off to again flow to the client120, and to a time during which the current mode host interface device110 allows the clock current ICLK and the data current IDATA to againflow to the client 120.

As shown in FIG. 11, a time period ‘trxd’ refers to a time during whichthe current mode host interface device 110 allows the reference currentIREF that was cut off to again flow to the client 120, and to a timeduring which the current mode client interface device 120 cuts off thereverse direction data current IR_DATA. A time period ‘ta’ refers to atime during which the current mode client interface device 120 cuts offthe reverse direction data current IR_DATA, and to the time during whichthe current mode host interface device 110 allows the data current IDATAto again flow to the client 120. The time period ‘ttxa’ should be longerthan a sum of the time period ‘trxd’ and the time period ‘ta’.

As described above, the current mode bus interface system according toan exemplary embodiment of the present invention includes a current modehost interface device and a current mode client interface device and iscapable of performing a bidirectional data transfer between the host andthe client. For example, the host is capable of transmitting data to theclient and receiving data from the client, and the client is capable oftransmitting data to the host and receiving data from the host.

Additionally, the method of performing the mode transition and the modecontrol signal generator according to an exemplary embodiment of thepresent invention are capable of performing a transition between anormal operation mode and a suspend mode in response to a wake-uprequest generated by the host or the client.

Therefore, the exemplary embodiments of the present invention may beused with various applications employing bidirectional communicationbetween hosts and clients, and with low-power applications such asmobile applications and devices such as portable camera phones, personaldigital assistants, etc.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A method of performing a mode transition in a current mode businterface system, the method comprising: cutting off transmittedcurrents from a host when the host enters into a suspend mode inresponse to a sleep request from the host; causing a client to enterinto a suspend mode when the client senses the cut-off of thetransmitted currents; and causing the host or the client to perform atransition from the suspend mode to a normal operation mode in responseto a wake-up request from the host or the client.
 2. The method of claim1, wherein the transmitted currents comprise a reference current, aclock current and a data current, and wherein the client enters into thesuspend mode when the client senses the cut-off of the referencecurrent.
 3. The method of claim 2, wherein causing the host and theclient to perform the transition comprises: transmitting the referencecurrent from the host in response to the wake-up request of the host,and wherein the client performs the transition from the suspend mode tothe normal operation mode when the client senses the reference currenttransmitted from the host.
 4. The method of claim 3, wherein the hosttransmits the clock current and the data current after the clientperforms the transition from the suspend mode to the normal operationmode.
 5. The method of claim 2, wherein causing the host and the clientto perform the transition comprises: transmitting a reverse directiondata current having a predetermined level from the client in response tothe wake-up request from the client; and transmitting the referencecurrent to the client after the host senses the reverse direction datacurrent received from the client, and wherein the client performs thetransition from the suspend mode to the normal operation mode when theclient senses the reference current transmitted from the host.
 6. Themethod of claim 5, wherein the host transmits the clock current and thedata current after the client performs the transition from the suspendmode to the normal operation mode.
 7. The method of claim 2, whereincausing the host and the client to perform the transition comprises:transmitting the reference current to the client from the host inresponse to the wake-up request from the host; transmitting the reversedirection data current to the host from the client via a conducting wireover which the data current is received, in response to the wake-uprequest of the client; and causing the client to perform a transitionfrom the suspend mode to a forward direction transfer mode after theclient stops the transmission of the reverse direction data current whenthe client senses the reference current transmitted from the host. 8.The method of claim 7, wherein the host transmits the clock current andthe data current after the client stops the transmission of the reversedirection data current to the host and performs the transition from thesuspend mode to the forward direction transfer mode.